Resistance heater for a pizza carton

ABSTRACT

In the fabrication of a resistance heater for a carton for packaging a pizza, an aluminum metallized sheet is adhered to a paperboard panel, a generally U-shaped strip of arc-sprayed zinc is applied to three edge portions of the upwardly facing electrically conductive metal layer of the metallized sheet, the interconnecting portion of the U-shaped strip and the immediately underlying metal layer are severed, and the metal layer is severed along a line extending adjacent the same interconnecting portion to the side thereof enclosed by the U-shaped strip, so that each of the severed sections of the interconnecting portion serves as a terminal for a corresponding leg portion of the U-shaped strip comprising the electrodes for the intermediate region of the metallized sheet.

This is a division of application Ser. No. 816,444, filed July 18, 1977,now U.S. Pat. No. 4,134,004, issued Jan. 9, 1979.

BACKGROUND OF THE INVENTION

This invention relates to packaging, and more particularly to animproved package for prepared hot foods, including heater means and amethod for its manufacture.

So-called take-out food restaurants have gained wide acceptance, and apopular food item is pizza. Characteristically, pizza is served atelevated temperatures that are difficult to maintain while it is beingtransported, frequently by automobile, from its place of purchase to itsplace of consumption.

It is a general objective of this invention to provide improved meansfor conveniently transporting foods at elevated, ready-to-servetemperatures.

It is a further and more specific objective to provide an improved pizzacarton and heater means for use therewith.

It is a still further objective of the invention to provide novel heatermeans adaptable for use in combination with a conventional pizza carton.

The invention has as a further objective a novel method for themanufacture of an electrical resistance heater.

It is another objective of the invention to provide heater means of anyof the aforementioned types that is capable of being energized throughthe cigarette lighter terminal of an automotive electrical circuit.

A still further objective of the invention is to provide an inexpensive,dispensible heater means of any of the aforementioned types.

SUMMARY OF THE INVENTION

In achievement of the foregoing as well as other objectives andadvantages, the invention contemplates, in its apparatus aspect, acarton having at least a bottom wall portion and a side wall portionextending transversely of the former, means defining an opening in saidside wall portion, and electrical heater means extending over saidbottom wall portion and including electrical terminal means disposed inregistry with said opening and presented for releasable engagement withelectrical connector means insertable through said opening to supplyelectrical energy for said heater means.

In its method aspect, the invention contemplates fabrication of theheater means by forming a sheet of electrically resistive material,laying down a conductive strip on said resistive material, said striphaving mutually spaced substantially parallel portions and aninterconnecting portion, and converting said parallel strip portionsinto electrodes for said electrically resistive material and saidinterconnecting strip portion into terminals for said electrodes bysevering said interconnecting portion and the immediately underlyingresistive material, and severing said resistive material along a regionadjacent said interconnecting strip portion and to the side thereofdisposed between said parallel strip portions.

The manner in which the foregoing as well as other objectives andadvantages of the invention may best be achieved will be more fullyunderstood from a consideration of the following description, taken inlight of the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partially exploded perspective view of carton and heaterstructure embodying the invention, with a portion broken away and thecarton cover in partially opened position for convenience ofillustration;

FIG. 2 is a perspective showing of the heater removed from the cartonseen in FIG. 1;

FIG. 3 is a sectional showing of the heater taken along the linesindicated generally by arrows 3--3 applied to FIG. 2;

FIG. 4 is a plan showing a terminal dip inserted into the carton.

FIG. 5 is a view looking in the direction of arrows 5--5 applied to FIG.4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference first to FIG. 1, a container and heater combinationcontemplated by the present invention comprises a carton 10, ofpaperboard or the like, for packaging food, such as, for example, apizza (not shown), and including spaced confronting top and bottom wallportions 12 and 13, respectively, and side wall portions 14. Withreference also to FIGS. 2 and 3, a resistance heater assembly 15contemplated by the invention comprises a corrugated paperboard panel 16having laminated thereto, by an adhesive 18, a sheet 17 comprising alayer of paper 20, such as, for example, glassine, provided with avacuum-metallized layer 21 of aluminum. Further to heater assembly 15, apair of bus bars 22, 23 extend over, and are disposed in electricalcontact with, metallized layer 21. Confronting portions 22a, 23a of thebus bars serve as electrode means for conducting electricity throughintermediate portions of layer 21 as the resistor element.

With reference to FIGS. 4 and 5, extended aligned portions 22b, 23b ofthe bus bars serve as terminals through which electrical energy issupplied to electrode means 22a, 23a, by a removable electricalconnector or terminal clip 24 that is connected to a suitable source ofelectrical energy and is extendable through an opening 25 provided inone of side wall portions 14, both electrically and mechanically toengage terminals 22b, 23b. One suitable source of energy is anautomotive cigarette lighter socket (12 V D.C.), not shown, into which aplug 34 (FIG. 1) is insertable for supplying energy through parallelwire conductor means 34a connected to the terminal clip.

As is seen also to advantage in FIGS. 1, 4 and 5, terminal clip 24 isgenerally rectangular in its cross section, having a main body portion27 of generally box shape and a wedge shaped portion 28 having its basecoplanar with the base of portion 27. Across the top of body portion 27is a projection 32 disposed and adapted, as is seen in FIG. 5, to bepushed past, and locked by abutting engagement with an inwardlypivotable flap 33 that initially extends (FIG. 1) over an upper portionof opening 25 in a side wall 14 of carton 10, upon sequential insertionof the wedge shaped portion 28 and the main body portion 27 through theopening 25. Access is gained to opening 25 by outward pivotation of aflap 35 (FIGS. 4 and 5) that initially extends over a lower portion ofthe opening (FIG. 1). Both flaps 33 and 35, and cut score linestherefor, conveniently are formed in a single die cutting operation. Theterminal clip 24 includes paired upper and lower spring contacts 36,36a, and 37, 37a as seen variously in FIGS. 1, 4 and 5. The uppercontacts 36 and 37 are disposed and adapted both electrically andfrictionally to engage terminal portions 22b, 23b of the bus bars uponinsertion of the clip to its locked position. The lower contacts 36a,37a frictionally engage the lower surface of corrugated panel 16 andenhance the described electrical engagement of the upper contacts 36,37. Also in locked position of the clip, its lower base portion restsupon the bottom wall 13 of the carton, beneath the corrugated panel 16.

A sheet of poly-coated paper 29, such as, for example locker wrap, madeup of layer 30 of paper and layer 31 of polyethylene as is seen in FIGS.3 and 5, conveniently is adhered, for example by a known heat seal,along the far edge of aluminum layer 21 as viewed in FIG. 2. Sheet 29extends over the heater, its electrodes and terminals, and the terminalclip, and slightly beyond the edge where electrical connection is made,so as to protect the underlying elements and aid in sealing opening 25,as is seen to advantage in FIG. 5.

In the method aspect of the invention, heater assembly 15 is formed bylaminating a sheet of aluminum-metallized glassine 17 onto a blank forcorrugated panel 16 by means of a layer of adhesive 18. One suchadhesive found suitable for this purpose is available from the MortonChemical Company under the trade designation Adcote 503H. Zinc metal isthen are sprayed in a generally U-shaped strip along three edges of themetallized layer 21 of sheet 17. A generally rectangular notch or gap 26(FIGS. 2, 4 and 5) is then die cut into panel 16, severing theinterconnecting loop portion of the arc-sprayed zinc strip and theimmediately underlying aluminum layer, followed by severing a portion ofmetallized layer 21 by making, for example, a knife or razor cut along aline designated generally by the numeral 38 and extending adjacent theloop portion of the strip to the side thereof between the spaced,confronting leg portions. Severing both the loop portion of the stripand the line portion of layer 21 transforms the strip portions 22a, 23a,into heater electrodes and portions 22b, 23b into heater electrodeterminals. The line of severance 38 precludes flow of electric currentdirectly from terminals 22b, 23b through metallized layer 21, ensuringflow instead through confronting spaced electrodes 22a, 23a and theportion of layer 21 therebetween.

In the disclosed preferred embodiment of the invention, the aluminumlayer 23 is about 200 Angstrom units in thickness, the distance betweenelectrodes 22a, 23a is about 121/2 inches, and the dimension of layer 21between razor cut 38 and its free edge is about 121/2 inches. It hasbeen found that application of about 12 volts D.C. to electrodes 22a,23a, disposed on an aluminum layer 21 of the dimensions described,achieved a satisfactory hold-warm operating condition of about 78 Watts,or about 1/2 Watt per sq. inch of heater surface. Advantageously, thethermally reflective characteristic of layer 21, taken with thethermally insulative characteristic of corrugated panel 16, serve tomaintain concentration of heat within the storage region of the cartonatop heater assembly 15.

It will be appreciated that the invention affords improved heatedpackage construction featured by its simple, inexpensive manufacture,and ready disposability upon use.

While preferred modes of laying down both the electrically resistive andelectrically conductive materials have been disclosed, as well aspreferred carton and heater base materials, it will be apparent to thoseskilled in the art that various changes and modifications can be madewithout departing from the scope of the appended claims.

We claim:
 1. In the fabrication of electrical resistance heater means,the method comprising: forming a sheet of electrically resistivematerial; laying down a strip of electrically conductive material onsaid sheet of electrically resistive material, in such a pattern thatsaid strip has mutually spaced substantially parallel portions and aninterconnecting portion; and converting said parallel strip portionsinto electrode means for said electrically resistive material and saidinterconnecting strip portions into terminal means for said electrodemeans by severing said interconnecting portion and said resistivematerial underlying same, and severing said resistive material along aregion adjacent said interconnecting strip portion and to the sidethereof disposed between said parallel strip portions.
 2. The methodaccording to claim 1, and further characterized in that said step offorming a sheet of electrically resistive material comprisesvacuum-metallizing a layer of a first metal onto a sheet of electricallyinsulative material, and said step of laying down a strip ofelectrically conductive material comprises arc-spraying a layer of asecond metal onto said first metal layer.
 3. The method according toclaim 2 and further characterized in that said step of severing saidinterconnecting strip portion and said underlying resistive material iseffected using die cutting procedures and the step of severing saidresistive material is effected by a knife cutting procedure.
 4. Themethod according to claim 3, wherein said first metal comprises aluminumand said second metal comprises zinc.